This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Selenium containing model compounds are useful for studying the structure of this important, bioactive substance. Trace amounts of Selenium are necessary for cellular function in most, if not all, animals, forming the active center of the enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants) and three known deiodinase enzymes (which convert one thyroid hormone to another). We performed X-band EPR measurements in order to determine whether or not paramagnetic Selenium complexes could be detected. Interpretation of the signal was complicated by the presence of significant amounts of a nuisance EPR signal from Mn(++) which dominated the spectral lineshape. Work is underway to improve sample preparation protocols to limit the amount of Mn(++) signal, after which we will revisit this system.